The molecular and crystal structure of (+)-2,3-trans-3,4-trans-leucocyanidin [(2R,3S,4R)-(+)-3,3′,4,4′,5,7-hexahydroxyflavan] dihydrate, and comparison of its heterocyclic ring conformation in solution and the solid state

Abstract

The crystal structure of (2R,3S,4R)-(+)-3,3′,4,4′,5,7-hexahydroxyflavan (1) dihydrate has been determined; the crystals are orthorhombic, space group P2₁2₁2₁, and have unit cell dimensions, a= 4.862(1), b= 15.796(4), c= 19.362(5)Å, U= 1 487.0(5)ų, Z= 4. The structure was solved by direct methods, refinements being to R= 0.031 for 1 247 independent reflections. The crystals are bound by two infinite networks of hydrogen bonds centred on the solvated water molecules. The conformation of the heterocyclic ring in the solid state is intermediate between a half-chair and a C(3)-sofa, whereas that in solution (acetone or water) is considered to be a C(2)-sofa.